Modified chitin for biocompatible dialysis membranes ii and process for preparation of modified cellulose and modified chitin for use therewith

ABSTRACT

A modified cellulose and/or chitin for biocompatible dialysis membranes having a structure represented by the formula ##STR1## wherein cell is unmodified cellulose or chitin, in each case without hydroxyl groups, s=3 in the case of cellulose and s=2 in the case of chitin, R&#39; is CH 3  and/or C 2  H 5  and/or C 3  H 7 , X denotes specified functional groups, m=0.75 to 2.85, and x=0.005 to 2.10. A process for preparation of the cellulose and/or chitin derivatives is also disclosed.

This is a division of application Ser. No. 07/315,574 filed Feb. 27, 1989, now U.S. Pat. No. 4,981,959.

TECHNICAL FIELD

The invention relates to cellulose and/or chitin derivatives which are suitable for the manufacture of biocompatible dialysis membranes.

BACKGROUND

U.S. Pat. No. 4,278,790 discloses cellulose solutions using lithium chloride and dimethyl acetamide as solvent. The solutions can contain up to 8% of lithium chloride and up to about 3% of cellulose. It is also possible to prepare cellulose derivatives in these cellulose solutions. According to this patent, the solutions are prepared by introducing cellulose into a mixture of dimethyl acetamide and lithium chloride and initially heating the mixture at about 150° C. for an extended period. Subsequently, the solution which has then formed is cooled to room temperature, while stirring.

In addition, German Offenlegungsschrift 3,312,022 and German Offenlegungsschrift 3,246,417 disclose cellulose ester filaments which are insoluble in water. They have an extremely high adsorptive capacity for water and physiological fluids. This may be an advantage for some areas of use but for many it is a disadvantage.

The cellulose acetate phthalates known from U.S. Pat. Nos. 2,759,925, 2,856,399 and 3,505,312 have high phthaloyl content and in salt form are water-soluble and therefore unsuitable as membrane materials. If the products are not in the salt form, they are insoluble in water and accordingly are also insoluble in the solvents which contain the usual hydrophilic additives and which are usual for membrane formation.

U.S. Pat. No. 3,745,202 and West German Offenlegungsschrift 2,300,496 describe processes for preparation of asymmetric membranes of cellulose derivatives having ester and/or ether groups.

U.S. Pat. No. 4,590,265 describes the products formed by oxidation of cellulose esters with ozone. The cellulose products synthesized by oxidation of cellulose or cellulose derivatives always had poor biocompatibility regardless of the oxidizing agent.

German Patent 2,705,735 discloses a dialysis membrane for hemodialysis, having antithrombogenic compounds chemically bonded thereto, the dialysis membrane consisting of two or more layers of a cellulose regenerated from cuprammonium cellulose solution, each of which has been obtained from separately fed orifices of a spinneret, which cellulose contains chemically bonded substances having antithrombogenic activity.

Japanese patent application 60-203,265 describes high molecular weight cellulose products for the preparation of medical instruments with anticoagulant properties. Such products are mixtures of polycationic and polyanionic cellulose derivatives, and are usually obtained by mixing appropriate polymer solutions. Such water-insoluble salts are unsuitable as membrane materials, since the danger is always present that they will be transformed by salt-interchange effects into a compound which is water-soluble or which swells greatly in water.

However, it has also been proposed in German Offenlegugnsschrift 1,720,087 that by reacting the polymeric material of the membrane with an alkyl halide and then reacting the resulting material with an alkali metal salt of an antithrombogenic compound having a cationic residue (for example, heparin or a heparinoid compound) the risk of blood coagulation is diminished. The possible alkyl halides in this context also include haloalkyldialkylamines. Cellulose, and most importantly cellulose acetate, are among the possible polymers.

An antithrombogenic effect of these known dialysis membranes is observed only when the degree of substitution of the modified cellulose is high, i.e., greater than at least 0.1, and a preheparinization with a relatively high heparin concentration (0.1 to 1% by weight solution) is carried out in a separate stage.

German Offenlegungsschrift 3,524,596 discloses a dialysis membrane with improved biocompatibility, which is distinguished in that the mean degree of substitution of a modified cellulose is 0.02 to 0.07. The known dialysis membrane composed of modified cellulose preferably contains such a modified cellulose which has a structure represented by the formula

    Cellulose-R'-X-Y

where

X represents --NR"-- and/or --N⁺ R"₂ -- and/or --S-- and/or --SO-- and/or --SO₂ -- and/or --CO--NR-- and/or --CO--O-- and/or --O--,

Y represents --R and/or --NR₂ and/or --Si(OR")₃ and/or --SO₃ H and/or --COOH and/or --PO₃ H₂ and/or --N⁺ HR₂ and the salts thereof,

R' represents an alkylene group and/or cycloalkylene group and/or arylene group having a total of 1 to 25C atoms,

R" represents a hydrogen atom or R, and

R represents an alkyl group having 1 to 5C atoms and/or a cycloalkyl group and/or aryl group.

This known dialysis membrane is capable of reducing to a considerable extent blood coagulation, leukopenia and complement activation. However, no noteworthy extent of adsorption of beta-2-microglobulin has been achieved.

German patent application P 3,723,897.3 describes cellulose derivatives having the general formula ##STR2## in which --Z-- denotes an alkylene, alkenylene, alkynylene, cycloalkylene or benzylene or xylylene radical which may or may not be substituted,

X denotes --H, --NR₂, --⁺ NR₃, --CN, --COOH, --SO₃ H, --PO(OR)₂, --CONR₂ or --Si(OR)₃, where R denotes a hydrogen atom or an alkyl or alkenyl group having 1 to 25C atoms, or a cycloalkyl, toluyl or phenyl group, and

Y is an alkyl, alkenyl or alkynyl group, which may or may not be substituted, having 1 to 36C atoms, a cycloalkyl group or a phenyl, toluyl or benzyl group or a ##STR3## or (--CH═CH--COOH) or NH--R radical and R has the same meaning, and r=1-20,

m=0-2.5,

n=0.2-2.95,

with the proviso that, where m=0, n≧1.55 when Y is an alkyl radical having 1-5C atoms, a --(CH₂)_(r) --COOH radical with r=0, 1 or 2 or a radical of phthalic acid, and the degree of polymerization is more than 400, and which can be prepared by homogeneous reaction in a mixture of dimethyl acetamide and/or N-methylpyrrolidone with LiCl after activation of the cellulose starting material without the presence of LiCl, the preparation thereof and the use thereof for membranes and filaments.

Apart from the circumstance that dialysis membranes composed of synthetic or natural polymers can, when used in artificial kidneys, very easily induce blood coagulation, which is substantially prevented by appropriate drug treatment, in the case of dialysis membranes composed of regenerated cellulose there is frequently a transient fall in leukocytes in the first period of dialysis treatment when a kidney patient is treated with dialyzers having cellulose membranes. This effect is called leukopenia. Leukopenia is a reduction in the number of leukocytes (white blood corpuscles) in the circulating blood. The number of white blood corpuscles in humans is about 4,000 to 12,000 cells/mm³.

Leukopenia associated with dialysis is most pronounced 15 to 20 min after the start, it being possible for the neutrophils (which are the leukocytes which can be stained with neutral or simultaneously with acidic and basic dyes) to disappear almost completely. Subsequently, the number of leukocytes recovers again within about one hour to almost the initial level or exceeds it.

If, after the leukocytes have recovered, a new dialyzer is connected, leukopenia occurs again to the same extent.

Cellulose membranes cause pronounced leukopenia. Even though the clinical significance of leukopenia has not been scientifically eludicated, there is nevertheless a desire for a dialysis membrane for hemodialysis which does not exhibit the leukopenic effect, without this adversely affecting the other very desired properties of dialysis membranes composed of regenerated cellulose.

During hemodialysis using membranes composed of regenerated cellulose, beside the leukopenia there has also been found a distinct complement activation. The complement system within the blood serum is a complex plasma-enzyme system which consists of many components and acts in various ways to prevent damage due to invading foreign cells (bacterial etc.). When antibodies against the invading organism are present, there can be complement-specific activation by the complex of the antibodies with antigenic structures of the foreign cells, otherwise complement activation takes place by an alternative pathway due to special surface features of the foreign cells. The complement system is based on a multiplicity of plasma proteins. After activation, these proteins react specifically in a defined sequence with one another and, finally, a cell-damaging complex which destroys the foreign cell is formed.

Individual components release peptides which induce inflammatory manifestations and occasionally can also have undesired pathological consequences for the organism. It is assumed that in the case of hemodialysis membranes composed of regenerated cellulose the activation takes place by the alternative pathway. These complement activations are detected objectively by determination of the complement fragments C3a and C5a.

In this context, reference is made to the following studies: D. E. Chenoweth et al., 24 Kidney International pages 746 et seq. (1983), and D. E. Chenoweth, 7 Asaio-Journal pages 44 et seq. (1984).

The carpal tunnel syndrome is affected by modified cellulose derivatives. Yet, there is a considerable need for further modifications of the cellulose in order to eliminate this phenomenon too as completely as possible.

An object of the present invention is to provide modified cellulose and/or chitin which, in terms of leukopenia, complement activation and blood coagulation, confers optimum properties on membranes and furthermore, is able to adsorb to a considerable extent the beta-2-microglobulin which is responsible for the carpal tunnel effect.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a modified cellulose and/or chitin of the formula ##STR4## wherein Cell is the framework of an unmodified cellulose molecule or of a chitin molecule, in each case without hydroxyl groups;

s=3 in the case of the unmodified cellulose molecule and s=2 in the case of the chitin molecule;

R' is at least one member selected from the group consisting of CH₃, C₂ H₅ and C₃ H₇ ;

X is at least one member selected from the group consisting of CO--R, CS--R, CO--CR"₂ --CO--CHR"₂, CO--OR, CONH--R, CONR"R, CSNH--R, CSNR"R, SO₂ --R, SO₂ NR"R, SO--R, SONR"R, PO₃ H₂, a salt of PO₃ H₂, PO₂ R"R, POR"₂, PO(OR")₂, CR"₂ --CR"(OH)--R, CR"₂ --CR"(SH)--R, CR"₂ -- CR"₂ --NHR, R--COOH, a salt of R--COOH, R--SO₃ H, a salt of R--SO₃ H, R, CH₂ --CH₂ --NR"₂, and CH₂ --CH₂ --SO₂ --R;

R is selected from the group consisting of alkyl, alkenyl, alkynyl, each of which is straight-chain or branched, unsubstituted, substituted by D, or the carbon chain is interrupted by a member selected from the group consisting of O, S, N, P, Si, CO-, and COO-groups, cycloalkyl which is unsubstituted, substituted by D, or contains a heteroatom selected from the group consisting of O, S, N, P and Si, arylalkyl, arylalkenyl, arylalkynyl, each of which is unsubstituted, substituted by D, or is interrupted by at least one heteroatom selected from the group consisting of O, S, N, P and Si, a bisaryl radical which is unsubstituted or substituted by D, a radical of a condensed aromatic compound which is unsubstituted or substituted by D, a radical of a heterocyclic compound which is unsubstituted or substituted by D, and aryl;

D is a member selected from the group consisting of R, --NR"₂, --⁺ NR"₃, --COOH or a salt thereof, --COOR", --CONR"₂, --CO--R", --CSOH, a salt of CSOH, --CSOR", --CSNR"₂, --SO₃ H, a salt of --SO₃ H, --SO₃ R", --SO₂ NR"₂, --SR", --SOR", --SONR"₂, --PO₃ H₂, a salt of--PO₃ H₂, --PO(OR")₂, --PO₂ H(NR"₂), --PO(NR"₂)₂, --PO₂ H₂, --POH(OR"), --CN, --NO₂, --OR", halogen, and --Si(OR")₃ ;

R" is H or R;

m=0.75 to 2.85; and

x=0.005 to 2.10.

The present invention also relates to a process for preparation of a modified cellulose, wherein one or more members of the group consisting of cellulose acetate, cellulose propionate, and cellulose butyrate having a degree of substitution of 0.75 to 2.85 are reacted with a member selected from the group consisting of acid chlorides, acid anhydrides, acids, esters, ketenes, diketenes, chloroformic acid esters, carbonic acid diesters, 2.5-diketooxazolidines, isatinic anhydride, isocyanates, carbamoyl chlorides, thiocyanates, thiocarbamoyl chlorides, sulfonyl chlorides, sulfonic acid anhydrides, N-chlorosulfonamides, sulfinic acid chlorides, N-chlorosulfinamides, phosphoric acid anhydride, phosphonic acid anhydrides, phosphonic acid chlorides, phosphorous acid, phosphinic acid anhydrides, ethylene oxide, ethylene sulfide, ethyleneimino, lactone, sultone, cleavable onium compounds, alkylaminoethanol sulfate esters, and alkylsulfonethanol sulfate esters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As summarized above, the objects of the present invention are achieved by a modified cellulose and/or chitin, wherein the modified cellulose and/or chitin has a structure represented by the formula ##STR5## wherein Cell is a framework of an unmodified cellulose molecule or of a chitin molecule, in each case without hydroxyl groups, s=3 in the case of the unmodified cellulose molecule and s=2 in the case of the chitin molecule;

R' is CH₃ and/or C₂ H₅ and/or C₃ H₇ ;

X is CO--R and/or CS--R and/or CO--CR"₂ --CO--CHR"₂ and/or CO--OR and/or CONH--R and/or CONR"R and/or CSNH--R and/or CSNR"R and/or SO₂ --R and/or SO₂ NR"R and/or SO--R and/or SONR"R and/or PO₃ H₂ or a salt thereof and/or PO₂ R"R and/or POR"₂ and/or PO(OR")₂ and/or CR"₂ --CR"(OH)--R and/or CR"₂ --CR"(SH)--R and/or CR"₂ -- CR"₂ --NHR and/or R--COOH of a salt thereof and/or R--SO₃ H or a salt thereof and/or R and/or CH₂ --CH₂ --NR"₂ and/or CH₂ --CH₂ --SO₂ --R;

R is an alkyl and/or alkenyl and/or alkynyl (straight-chain and/or branched, which may or may not be substituted, the carbon chain also being able to be interrupted by heteroatoms such as O, S, N, P or Si as well as by CO- or COO-groups) and/or cycloalkyl (which may or may not contain heteroatoms and/or may or may not be substituted) and/or aryl and/or arylalkyl and/or arylalkenyl and/or arylalkynyl (which may or may not contain heteroatoms and/or may or may not be substituted) and/or bisaryl radical (which may or may not be substituted) and/or radical of a condensed aromatic compound (which may or may not be substituted) and/or radical of a heterocyclic compound (which may or may not be substituted);

By "substituted", there are meant, in addition to radicals in the sense of R, also the following groups:

--NR"₂, and/or --N+R", and/or --COOH or a salt thereof, and/or --COOR", and/or --CONR", and/or --CO--R", and/or --CSOH or a salt thereof, and/or --CSOR", and/or --CSNR"₂, and/or --SO₃ H or a salt thereof, and/or --SO₃ R", and/or --SO₂ NR"₂, and/or --SR", and/or --SOR", and/or --SONR"₂, and/or --PO₃ H₂ or a salt thereof, and/or --PO(OR")₂, and/or --PO₂ H(NR"₂), and/or --PO(NR"₂)₂, and/or --PO₂ H₂, and/or --POH(OR"), and/or --CN, and/or --NO₂, and/or --OR", and/or halogen, and/or --Si(OR")_(3;)

R" is H or R;

m=0.75 to 2.85;

x=0.005 to 2.10.

Preferably the degree of polymerization is 100 to 500, especially 150 to 350. Modified celluloses in which m=1.00 to 2.50 and x =0.01 to 0.45 are also preferred.

Modified celluloses in which R' denotes CH₃ are especially preferred.

If m =1.10 to 2.35, modified celluloses are obtained which are characterized by exhibiting a pronounced reduction of the C5a activation.

The subject matter of the invention is also a process for preparation of the modified celluloses according to the invention, wherein cellulose acetate and/or cellulose propionate and/or cellulose butyrate having a degree of substitution of 0.75 to 2.85 are reacted with acid chlorides and/or acid anhydrides and/or acids and/or esters and/or ketenes and/or diketenes and/or chloroformic acid esters and/or carbonic acid diesters and/or 2.5-diketooxazolidines and/or isatinic anhydride and/or isocyanates and/or carbamoyl chlorides and/or thiocyanates and/or thiocarbamoyl chlorides and/or sulfonyl chlorides and/or sulfonic acid anhydrides and/or N-chlorosulfonamides and/or sulfinic acid chlorides and/or N-chlorosulfinamides and/or phosphoric acid anhydride and/or phosphonic acid anhydrides and/or phosphonic acid chlorides and/or phosphorous acid and/or phosphinic acid anhydrides and/or ethylene oxide and/or ethylene sulfide and/or ethyleneimino and/or lactone and/or sultone and/or cleavable onium compounds and/or alkylaminoethanol sulfate esters and/or alkylsulfonethanol sulfate esters.

The complement activation within the scope of the present invention was assessed on the basis of the C5a fragments. For this purpose, 300 ml of heparinized blood plasma was recirculated in vigro through a dialyzer with an effective exchange area of 1 m² at a plasma flow rate of 100 ml/min for a period of 4 hours. The C5a fragments in the plasma were determined using the RIA method (Upjohn assay). The relative complement activation for the particular time of measurement was calculated as a percentage by forming the ratio of the concentration at the time of sampling with the initial value. The measurement after a recirculation time of 4 hours was used for the evaluation. Flat membranes were incubated with heparinized blood plasma for 3 hours and then the C5a fragments were determined.

The increase in the beta-2-microglobulin level in long-term dialysis patients is observed after use of membranes composed of regenerated cellulose and is attributed to these membranes being less permeable to substances in the molecular weight range 1,000 to 20,000 and the microglobulins thus being removed to an insufficient extent during the dialysis. Beta-2-microglobulin is not adsorbed to a noteworthy extent onto customary membranes composed of regenerated cellulose. However, the cellulose derivatives according to the invention can contribute in an unexpected manner to this.

The beta-2-microglobulin content adsorbed onto the membrane is measured within the scope of the invention in the following manner.

10 ml of human blood plasma are added to each 500 mg of substance (dialysis membrane) and incubated at 37° C. for 30 minutes. The human blood plasma contains 13.67 mg/liter of beta-2-microglobulin. The sample is centrifuged at 3,000 r.p.m. for 15 minutes The beta-2-microglobulin content in the supernatant is determined The sample is then washed 2 times with 10 ml of phosphate-buffered saline each time. The microglobulin content in the washings is also determined. The percentage amount of beta-2-microglobulin adsorbed can be calculated from the difference between the original and the unabsorbed beta-2-microglobulin.

The average degree of polymerization DP was determined in a cupriethylenediamine solution by the DIN 54270 method.

The degree of etherification and/or degree of esterification were determined on the basis of the analytical results which are known and typical for the substituents, for example nitrogen by the Kjeldahl method, sulfur by the Schoniger method or phosphorus by the molybdate method, where appropriate from the difference between before and after saponification.

EXAMPLES

The Examples set forth below illustrate the practice and advantages of the present invention. As Examples, they are illustrative only, and should not be construed to limit the allowable scope of protection available to the Applicant in any way whatsoever.

EXAMPLE 1

50.88 g (0.2 mole) of cellulose-2.2-acetate were dissolved in 500 ml of dimethyl acetamide in a 1 liter three-necked flask. 5 g (0.05 mole) of potassium acetate (catalyst) and 26.6 g (0.10 mole) of dodecenylsuccinic anhydride were added to the clear viscous solution and heated at 70° C. for 20 hours. After cooling, the reaction product was precipitated with water, washed with alcohol and dried in a vacuum oven at 60° C. This procedure yielded 50.5 g of a cellulose mixed ester having the following specifications:

Contents of acetyl groups m=2.2

Content of dodecenylsuccinate groups: x=0.08

Degree of polymerization: DP=340

47 g of the cellulose-2.2-acetate-0.08-dodecenylsuccinate were dissolved in 365 g of formic acid. Thereafter the solution was diluted with 50 g of water and 60 g of PEG 400, filtered, deaerated and spun to capillary membranes by a known procedure. i-Propyl myristate was used as the lumen filling. The capillary membranes had the following properties:

Wall thickness: 11 μm

Internal diameter: 200 μm

Ultrafiltration rate: 5 7 ml/h×m² ×mm Hg at 37° C.

Vitamin B12 permeability 6.2×10⁻³ cm/min at 37° C.

Beta-2-microglobulin adsorption: 30%

The complement activation with the above-mentioned cellulose derivative membrane is less than that with unmodified cellulose membranes. The reduction in C5a compared with the unmodified cellulose membrane is 98%.

EXAMPLE 2

267 g (1 mole) of cellulose-2.5-acetate were dissolved in 2,300 ml of acetone in a 4 liter three-necked flask. 58.86 g (0.6 mole) of potassium acetate (catalyst) and 136.8 g (1.2 mole) of glutaric anhydride were added to the clear viscous solution and the mixture was heated under reflux for 48 hours. After cooling, the reaction product was precipitated with water, washed with alcohol and dried in a vacuum oven at 60° C. This procedure yielded 280 g of a cellulose mixed ester having the following specifications:

Content of acetyl groups m=2.35

Content of glutarate groups: x=0.18

Degree of polymerization: DP=350

The mixed ester was dissolved in a mixture of formic acid, polyethylene glycol 400 and water (78:15:7) and processed to flat membranes. The reduction in C5a compared with the unmodified cellulose membrane is 100%.

EXAMPLES 3-15

On the basis of the procedure of Example 1 or 2, a series of cellulose acetate derivatives was synthesized in dimethyl acetamide and processed by known methods to flat membranes, and their complement activation was determined on the basis of the C5a fragments as well as their beta-2-microglobulin adsorption capacity. The results are listed in Table 1.

EXAMPLE 16

47.94 g (0.2 mole) of cellulose-1.85-acetate were dissolved in 400 ml of formic acid in a 1 liter three-necked flask. 9.81 g (0.1 mole) of potassium acetate (catalyst) and 13.00 g (0.1 mole) of propionic anhydride were added to the clear viscous solution, and the mixture was stirred at 50° C. for 2 hours. Thereafter 9.80 g (0.10 mole) of maleic anhydride were added and the reaction mixture was stirred at 50° C. for a further 2 hours. After cooling to 20° C., the reaction solution was diluted with 30 ml of water and 40 ml of glycerol, filtered, deaerated and spun to hollow filaments. The cellulose mixed ester membranes obtained in this way had the following properties:

Degree of polymerization: DP=270

Content of acetyl/propionyl groups: m=1.85/0.3

Content of maleate groups: x=0.12

Wall thickness: 10 μm

Internal diameter: 200 μm

Ultrafiltration rate: 4.5 ml/h m2.mm Hg at 37° C.

Vitamin B12 permeability: 4.9×10⁻³ cm/min at 37° C.

Beta-2-microglobulin adsorption: 26%

The reduction in C5a compared with the unmodified cellulose membrane is 97%.

EXAMPLE 17

50.88 g (0.2 mole) of cellulose-2.2-acetate were dissolved in 400 ml of acetone in a 1 liter three-necked flask. 9.81 g (0.1 mole) of potassium acetate (catalyst) and 18.4 g (0.10 mole) of sebacic anhydride were added to the clear viscous solution and the mixture was heated under reflux for 24 hours. After cooling to 20° C., the reaction solution was diluted with 50 ml of water and 60 ml of glycerol, filtered, deaerated and spun to capillary membranes. These had the following properties:

Degree of polymerization: DP=290

Content of acetyl groups: m=2.20

Content of sebacyl groups: x=0.07

Wall thickness: 12 μm

Internal diameter: 205 μm

Ultrafiltration rate: 5.1 ml/h×m² ×mm Hg at 37° C.

Vitamin B12 permeability: 5.3×10⁻³ cm/min at 37° C.

Beta-2-microglobulin adsorption: 27%

The reduction in C5a compared with the unmodified cellulose membrane is 89%.

EXAMPLE 18

51.72 g (0.2 mole) of cellulose-2.3-acetate (DP =250) were dissolved in 500 ml of dimethyl acetamide in a 1 liter three-necked flask 16.66 g (0.14 mole) of phenyl isocyanate and 3.03 g (0.03 mole) of triethylamine (catalyst) were added to the clear viscous solution. To complete the reaction, the mixture was kept at 90° C. for 10 hours and further stirred at 20° C. for 15 hours. The reaction product was precipitated with methanol, washed with cold and hot methanol and dried in a vacuum oven at 60° C. This procedure yielded 52 8 g of a cellulose ester carbamate having the following specifications:

Content of acetyl groups: m=2.25

Content of phenylcarbamate groups: x=0.14

47 g of the cellulose-2.25-acetate-0.14-phenylcarbamate were dissolved in 365 g of formic acid. Thereafter the solution was diluted with 50 g of water and 60 g of PEG 400, filtered, deaerated and spun to capillary membranes by a known procedure. These had the following properties:

Wall thicknesses: 10 μm

Internal diameter 200 μm

Ultrafiltration rate: 6.3 ml/h×m² ×mm Hg at 37° C.

Vitamin B12 permeability: 6.5×10⁻³ cm/min at 37° C.

The reduction in C5a compared with the unmodified cellulose membrane is 100%.

EXAMPLE 19

333.75 (1.25 mole) of cellulose-2.5-acetate were suspended in 4000 ml of toluene in a 6 liter three-necked flask. Thereafter 100 g (0.75 mole) of p-tolyl isocyanate and 110 g (1.39 mole) of pyridine were added and the mixture was heated under reflux for 48 hours. After cooling, the reaction product was filtered off, washed with toluene and ethanol and dried in a vacuum oven at 60° C.

Yield: 375 g

Content of acetyl groups: m=2.34

Content of tolylcarbamate groups: x=0.39

The product synthesized in this was dissolved in a mixture of formic acid, polyethylene glycol 400 and water (78:15:7) and processed to flat membranes. The reduction in C5a compared with the unmodified cellulose membrane is 100%.

EXAMPLES 20-30

In analogy to the procedure of Example 18 or 19, several cellulose acetate derivatives were synthesized and processed by known methods to flat membranes, and their complement activation was determined on the basis of the C5a fragments. The results are listed in Table 2.

EXAMPLE 31

51.72 g (0.2 mole) of cellulose-2 3-acetate were dissolved in 500 ml of pyridine in a 1 liter three-necked flask. 99.5 g (0.3 mole) of chloroformic acid octadecyl ester were added to the solution, and the mixture was kept at 100° C. for 6 hours and at 20° C. for 15 hours. The reaction product was precipitated with methanol, washed with water and ethanol and dried in a vacuum oven at 60° C. This procedure yielded 54.2 g of a cellulose ester having the following specifications:

Content of acetyl groups m=2.26

Content of octadecyl carbonate groups x=0.06

Degree of polymerization: DP=240

For the flat membranes prepared from this cellulose acetate derivative by known methods, the reduction in C5a compared with the unmodified cellulose membrane is 92%.

EXAMPLES 32-42

On the basis of the procedure of Example 31, the cellulose derivatives listed in Table 3 were prepared and processed by known methods to flat membranes, and their biocompatibility properties were examined.

EXAMPLE 43

52.54 g (0.20 mole) of cellulose-2 0-acetate-0.3-propionate (DP=220) were suspended in 500 ml of toluene in a 1 liter three-necked flask. 33.76 g (0.16 mole) of ethyleneiminosuccinic acid diethyl ester and 3.84 g (0.04 mole) of methanesulfonic acid were added to the suspension. To complete the reaction, the mixture was heated under reflux for 6 hours and further stirred at 20° C. for 15 hours. The reaction mixture was mixed with ethanol, and the reaction product was suction-filtered, washed with ethanol and dried in a vacuum oven at 60° C. This procedure yielded 50.6 g of a cellulose ester ether having the following specifications:

Content of acetyl/propionyl groups: m=2.0/0.3

Content of ethylaminosuccinic acid diethyl ester groups: x=0.08

For flat membranes prepared by known methods, the reduction in C5a compared with the unmodified cellulose membrane is 70%.

EXAMPLES 44-48

On the basis of the procedure of Example 43, the cellulose derivatives listed in Table 4 were synthesized and their C5a activation was determined.

EXAMPLE 49

534 g (2 mole) of cellulose-2.5-acetate were dissolved in 4,000 ml of acetone in a 6 liter three-necked flask. 437 g (2 mole) of lauric acid chloride and 294 g of potassium acetate were added to the clear viscous solution and the mixture was heated under reflux for 48 hours. The reaction product was precipitated with water, washed with alcohol and dried in a vacuum oven at 60° C. This procedure yielded 548 g of a cellulose mixed ester having the following specifications:

Content of acetyl groups m=2.38

Content of lauroyl groups: x=0.08

Flat membranes were prepared from this mixed ester by known methods, and their complement activation was determined on the basis of the C5a fragments. The reduction in C5a compared with the unmodified cellulose membrane is 100%.

EXAMPLE 50

In analogy to the procedure of Example 49, a cellulose mixed ester with the following specifications was obtained by reaction of cellulose-2.5-acetate with stearic acid chloride:

Content of acetyl groups m=2.34

Content of stearoyl groups: x=0.05

Flat membranes prepared by known methods have no C5a activation.

                                      TABLE 1                                      __________________________________________________________________________                                               % beta-2                                                                    %  micro-                               Example                                C5a                                                                               globulin                             No.  R'    m    X              x    DP red.                                                                              absorption                           __________________________________________________________________________      3   CH.sub.3                                                                             2.2  C.sub.15 H.sub.31 CH═C(CH.sub.2 COOH)CO                                                   0.08 300                                                                                98                                                                               31                                    4   CH.sub.3                                                                             2.2  C.sub.18 H.sub.37 NHC.sub.6 H.sub.4 CO                                                        0.06 310                                                                                95                                                                               --                                    5   CH.sub.3                                                                             2.35 HOOCC.sub.6 H.sub.4 CO                                                                        0.40 220                                                                               100                                                                               70                                    6   CH.sub.3 /C.sub.2 H.sub.5                                                            2.0/0.30                                                                            HOOCC.sub.6 H.sub.4 CO                                                                        0.13 210                                                                                92                                                                               --                                    7   CH.sub.3                                                                             2.35 HOOCCH═CHCO                                                                               0.11 330                                                                                98                                                                               30                                    8   CH.sub.3                                                                             2.35 HOOCC.sub.2 H.sub.4 CO                                                                        0.12 305                                                                               100                                                                               --                                    9   CH.sub.3                                                                             2.0  HOOCCH(SO.sub.3 H)CH.sub.2 CO                                                                 0.08 215                                                                                94                                                                               45                                   10   CH.sub.3                                                                             2.2  HOOCCH(Cl)CH.sub.2 CO                                                                         0.09 280                                                                                89                                                                               --                                   11   CH.sub.3                                                                             2.05 C.sub.17 H.sub.35 COCH(C.sub.16 H.sub.33)CO                                                   0.05 210                                                                               100                                                                               --                                   12   CH.sub.3 /C.sub.3 H.sub.7                                                            2.0/0.2                                                                             HOOCC.sub.3 H.sub.6 CO                                                                        0.10 225                                                                                97                                                                               37                                   13   CH.sub.3                                                                             2.0  C.sub.17 H.sub.33 CO/C.sub.6 H.sub.5 NHCO                                                     0.04/0.11                                                                           --  98                                                                               --                                   14   CH.sub.3                                                                             2.0  C.sub.11 H.sub.23 CO/HOOCC.sub.2 H.sub.4 CO                                                   0.10/0.08                                                                           210                                                                                96                                                                               28                                   15   CH.sub.3                                                                             2.2  C.sub.18 H.sub.37 OCOCH═CHCO                                                              0.07 270                                                                                95                                                                               --                                   __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________                                               %                                    Example                                   C5a                                  No.  R'    m    X                    x    red.                                 __________________________________________________________________________     20   CH.sub.3                                                                             2.35 C.sub.4 H.sub.9 NHCO 0.26 100                                  21   CH.sub.3                                                                             2.35 C.sub.6 H.sub.11 NHCO                                                                               0.12  98                                  22   CH.sub.3                                                                             2.3  ClC.sub.6 H.sub.4 NHCO                                                                              0.35 100                                  23   CH.sub.3                                                                             2.3  C.sub.18 H.sub.37 NHCS                                                                              0.07  80                                  24   CH.sub.3                                                                             2.3  C.sub.6 H.sub.5 CH.sub.2 CO/C.sub.6 H.sub.5 NHCO                                                    0.05/0.14                                                                           100                                  25   CH.sub.3                                                                             2.3  C.sub.18 H.sub.37 CO/CH.sub.3 C.sub.6 H.sub.4 NHCO                                                  0.06/0.09                                                                            98                                  26   CH.sub.3                                                                             2.3  C.sub.11 H.sub.23 CH═C(CH.sub.2 COOH)CO/C.sub.65                                                0.07/0.10                                                                           100                                  27   CH.sub.3                                                                             2.3  HOOCC.sub.2 H.sub.4 CO/C.sub.18 H.sub.37 NHCO                                                       0.09/0.05                                                                            96                                  28   CH.sub.3 /C.sub.2 H.sub.5                                                            2.0/0.30                                                                            HOOCC.sub.6 H.sub.4 CO/CH.sub.3 C.sub.6 H.sub.4 NHCO                                                0.10/0.09                                                                            98                                  29   CH.sub.3 /C.sub.3 H.sub.7                                                            2.0/0.2                                                                             C.sub.17 H.sub.33 CO/C.sub.6 H.sub.11 NHCO                                                          0.05/0.10                                                                            97                                  30   CH.sub.3                                                                             2.3  C.sub.11 H.sub.23 COCH(C.sub.10 H.sub.21)CO/C.sub.6                            H.sub.5 NHCO         0.06/0.12                                                                            98                                  __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________                                        %                                           Example                            C5a                                         No.  R'    m    X             x    red.                                        __________________________________________________________________________     32   CH.sub.3                                                                             2.3  C.sub.18 H.sub.37 N(C.sub.4 H.sub.9)CO                                                       0.07  92                                         33   CH.sub.3                                                                             2.3  C.sub.18 H.sub.37 OCH.sub.2                                                                  0.08  89                                         34   CH.sub.3                                                                             2.3  C.sub.6 H.sub.5 SO.sub.2                                                                     0.10  84                                         35   CH.sub.3                                                                             2.3  C.sub.18 H.sub.37 N(CH.sub.3)SO.sub.2                                                        0.06  90                                         36   CH.sub.3                                                                             2.3  C.sub.18 H.sub.37 OCH.sub.2 NHCS                                                             0.07  86                                         37   CH.sub.3 /C.sub.2 H.sub.5                                                            2.3/0.30                                                                            C.sub.18 H.sub.37 OCH.sub.2 NHCO                                                             0.05  94                                         38   CH.sub.3 /C.sub.2 H.sub.5                                                            2.0/0.30                                                                            C.sub.12 H.sub.25 SO.sub.2                                                                   0.06  88                                         39   CH.sub.3                                                                             2.3  HOOCC.sub.2 H.sub.4                                                                          0.12  90                                         40   CH.sub.3                                                                             2.3  HOOCC.sub.2 H.sub.4 /C.sub.16 H.sub.33 NHCO                                                  0.09/0.05                                                                            97                                         41   CH.sub.3                                                                             2.3  HO.sub.3 SC.sub.3 H.sub.6                                                                    0.10  95                                         42   CH.sub.3                                                                             2.3  C.sub.17 H.sub.33 CO/HO.sub.3 SC.sub.3 H.sub.6                                               0.05/0.08                                                                            93                                         __________________________________________________________________________

                                      TABLE 4                                      __________________________________________________________________________                                        %                                           Example                            C5a                                         No.  R'    m    X             x    red.                                        __________________________________________________________________________     44   CH.sub.3                                                                             2.30 CH.sub.2 CH(OH)CH.sub.2 N(C.sub.2 H.sub.5).sub.2                                             0.10 85                                          45   CH.sub.3 /C.sub.3 H.sub.7                                                            2.0/0.30                                                                            CH.sub.2 CH(OH)CH.sub.2 N(C.sub.2 H.sub.5).sub.2                                             0.12 89                                          46   CH.sub.3                                                                             2.30 CH.sub.2 CH(OH)CH.sub.2 SO.sub.2 C.sub.18 H.sub.37                                           0.05 73                                          47   CH.sub.3                                                                             2.30 CH.sub.2 CH(SH)CH.sub.3                                                                      0.08 76                                          48   CH.sub.3                                                                             2.30 C.sub.2 H.sub.4 NH.sub.2                                                                     0.08 79                                          __________________________________________________________________________ 

What is claimed is:
 1. A modified chitin, wherein the modified chitin has a structure represented by the formula ##STR6## wherein Cell is the framework of a chitin molecule, without hydroxyl groups;s=2; R' is at least one member selected from the group consisting of CH₃, C₂ H₅ and C₃ H₇ ; X is at least one member selected from the group consisting of CO--R, CS--R, CO--CR"₂ --CO--CHR"₂, CO--OR, CONH--R, CONR"R, CSNH--R, CSNR"R, SO₂ --R, SO₂ NR"R, SO--R, SONR"R, PO₃ H₂, a salt of PO₃ H₂, PO₂ R"R, POR"₂, PO(OR")₂, CR"₂ --CR"(OH)--R, CR"₂ --CR"(SH)--R, CR"₂ --CR"₂ --NHR, R--COOH, a salt of R--COOH, R--SO₃ H, a salt of R--SO₃ H, R, CH₂ --CH₂ --NR"₂, and CH₂ --CH₂ --SO₂ --R; R is selected from the group consisting of alkyl, alkenyl and alkynyl, each of which may be straight-chain having a carbon chain length of from 1 to 18 carbon atoms, unsubstituted, substituted by D, or the carbon chain is interrupted by a member selected from the group consisting of O, S, N, P, Si, CO-, and COO-groups, cycloalkyl which is unsubstituted, substituted by D, or contains a heteroatom selected from the group consisting of O, S, N, P and Si, arylalkyl, arylalkenyl, arylalkynyl, each of which is unsubstituted, substituted by D, or is interrupted by at least one heteroatom selected from the group consisting of O, S, N, P and Si, a bisaryl radical which is unsubstituted or substituted by D, a radical of a condensed aromatic compound which is unsubstituted or substituted by D, a radical of a heterocyclic compound which is unsubstituted or substituted by D, and aryl; D is a member selected from the group consisting of R, --NR"₂, --⁺ NR"₃, --COOH, or a salt of thereof, COOR", --CONR"₂, --CO-- R", --CSOH, or a salt of --CSOH, --CSOR", --CSNR"₂, --SO₃ H, a salt of --SO₃ H, --SO₃ R", --SO₂ NR"₂, --SR", --SOR", --SONR"₂, --PO₃ H₂, a salt of --PO₃ H₂, --PO(OR")₂, --PO₂ H(NR"₂), --PO(NR"₂)₂, --PO₂ H₂, --POH(OR"), --CN, --NO₂, --OR", halogen, and --Si(OR")₃ ; R" is H or R; m=0.75 to 2.85; and x=0.005 to 2.10.
 2. A modified chitin as claimed in claim 1 wherein the degree of polymerization is 100 to
 500. 3. A modified chitin as claimed in claim 2, wherein the degree of polymerization is 150 to
 350. 4. A modified chitin as claimed in claim 3, wherein m=1.0 to 2.50 and x=0.05 to 0.45.
 5. A modified chitin as claimed in claim 3, wherein R' is CH₃.
 6. A modified chitin as claimed in claim 1, wherein m=1.10 to 2.35.
 7. A process for preparing at least one compound selected from the group consisting of a modified cellulose and chitin, wherein said modified cellulose and chitin have a structure represented by the formula: ##STR7## wherein, Cell is the framework of an unmodified cellulose molecule or of a chitin molecule, in each case without hydroxyl groups;s=3 in the case of the unmodified cellulose molecule and s=2 in the case of the chitin molecule; R' is at least one member selected from the group consisting of CH₃, C₂ H₅, and C₃ H₇ ; X is at least one member selected from the group consisting of CO--R, CS--R, CO--CR"₂ --CO--CHR"₂, CO-OR, CONH--R, CONR"R, CSNH--R, CSNR"R, SO₂ --R, SO₂ NR"R, SO--R, SONR"R, PO₃ H₂, a salt of PO₃ H₂, PO₂ R"R, POR"₂, PO(OR")₂, CR"₂ --CR"(OH)--R, CR"₂ --CR"(SH)--R, CR"₂ --CR"₂ --NHR, R--COOH, a salt of R--COOH, R--SO₃ H, a salt of R--SO₃ H, R, CH₂ --CH₂ --NR"₂, and CH₂ --CH₂ --SO₂ --R; R is selected from the group consisting of alkyl, alkenyl and alkynyl, each of which may be straight-chain having a carbon chain length of from 1 to 18 carbon atoms, unsubstituted, substituted by D or the carbon chain is interrupted by a member selected from the group consisting of O, S, N, P, Si, CO-- and COO-- groups, cycloalkyl which is unsubstituted, substituted by D or contains a heteroatom selected from the group consisting of O, S, N, P, Si, arylalkyl, arylalkenyl, arylalkynyl, each of which is unsubstituted, substituted by D, or is interrupted by at least one heteroatom selected from the group consisting of O, S, N, P, and Si, a bisaryl radical which is unsubstituted or substituted by D, a radical of a condensed aromatic compound which is unsubstituted or substituted by D, a radical of a heterocyclic compound which is unsubstituted or substituted by D, and aryl; D is a member selected from the group consisting of R, --NR"₂, --⁺ NR"₃, --COOH or a salt thereof, --COOR", --CONR"₂, --CO--R", --CSOH, or a salt of --CSOH, --CSOR", --CSNR"₂, --SO₃ H, a salt of --SO₃ H, --SO₃ R", --SO₂ NR"₂, --SR", --SOR", --SONR"₂, --PO₃ H₂, a salt of --PO ₃ H₂, --PO(OR")₂, --PO₂ H(NR"₂), --PO(NR"₂)₂, --PO₂ H₂, --POH(OR"), --CN, --NO₂, --OR", halogen, and --Si(OR")₃ ; R" is H or R; m=0.75 to 2.85; and x=0.005 to 2.10,wherein one or more members of the group consisting of cellulose acetate, cellulose propionate, and cellulose butyrate having a degree of substitution of 0.75 to 2.85 are reacted with a member selected from the group consisting of acid chlorides, acid anhydrides, acids, esters, ketenes, diketenes, chloroformic acid esters, carbonic acid diesters, 2.5 diketooxazolidines, isatinic anhydride, isocyanates, carbamoyl chlorides, thiocyanates, thiocarbamoyl chlorides, sulfonyl chlorides, sulfonic acid anhydrides, N-chlorosulfonamides, sulfinic acid chlorides, N-chlorosulfinamides, phosphoric acid anhydride, phosphonic acid anhydrides, phosphonic acid chlorides, phosphorous acid, phosphinic acid anhydrides, ethylene oxide, ethylene sulfide, ethyleneimino, lactone, sultone, cleavable onium compounds, alkylaminoethanol sulfate esters, and alkylsulfonethanol sulfate esters to form said compound, and isolating said compound. 